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Role of soil pH in the development of enhanced biodegradation of fenamiphos.

ABSTRACT: Repeated treatment with fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) resulted in enhanced biodegradation of this nematicide in two United Kingdom soils with a high pH (>/= 7.7). In contrast, degradation of fenamiphos was slow in three acidic United Kingdom soils (pH 4.7 to 6.7), and repeated treatments did not result in enhanced biodegradation. Rapid degradation of fenamiphos was observed in two Australian soils (pH 6.7 to 6.8) in which it was no longer biologically active against plant nematodes. Enhanced degrading capability was readily transferred from Australian soil to United Kingdom soils, but only those with a high pH were able to maintain this capability for extended periods of time. This result was confirmed by fingerprinting bacterial communities by 16S rRNA gene profiling of extracted DNA. Only United Kingdom soils with a high pH retained bacterial DNA bands originating from the fenamiphos-degrading Australian soil. A degrading consortium was enriched from the Australian soil that utilized fenamiphos as a sole source of carbon. The 16S rRNA banding pattern (determined by denaturing gradient gel electrophoresis) from the isolated consortium migrated to the same position as the bands from the Australian soil and those from the enhanced United Kingdom soils in which the Australian soil had been added. When the bands from the consortium and the soil were sequenced and compared they showed between 97 and 100% sequence identity, confirming that these groups of bacteria were involved in degrading fenamiphos in the soils. The sequences obtained showed similarity to those from the genera Pseudomonas, Flavobacterium, and CAULOBACTER: In the Australian soils, two different degradative pathways operated simultaneously: fenamiphos was converted to fenamiphos sulfoxide (FSO), which was hydrolyzed to the corresponding phenol (FSO-OH) or was hydrolyzed directly to fenamiphos phenol. In the United Kingdom soils in which enhanced degradation had been induced, fenamiphos was oxidized to FSO and then hydrolyzed to FSO-OH, but direct conversion to fenamiphos phenol did not occur.

SUBMITTER: Singh BK

PROVIDER: S-EPMC309955 | biostudies-literature | 2003 Dec

REPOSITORIES: biostudies-literature

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Role of soil pH in the development of enhanced biodegradation of fenamiphos.

Singh Brajesh K BK Walker Allan A Morgan J Alun W JA Wright Denis J DJ

Applied and environmental microbiology 20031201 12

Repeated treatment with fenamiphos (ethyl 4-methylthio-m-tolyl isopropylphosphoramidate) resulted in enhanced biodegradation of this nematicide in two United Kingdom soils with a high pH (>/= 7.7). In contrast, degradation of fenamiphos was slow in three acidic United Kingdom soils (pH 4.7 to 6.7), and repeated treatments did not result in enhanced biodegradation. Rapid degradation of fenamiphos was observed in two Australian soils (pH 6.7 to 6.8) in which it was no longer biologically active ag ...[more]

PMID: 14660347

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Project description:We examined the role of microorganisms in the degradation of the organophosphate insecticide chlorpyrifos in soils from the United Kingdom and Australia. The kinetics of degradation in five United Kingdom soils varying in pH from 4.7 to 8.4 suggested that dissipation of chlorpyrifos was mediated by the cometabolic activities of the soil microorganisms. Repeated application of chlorpyrifos to these soils did not result in the development of a microbial population with an enhanced ability to degrade the pesticide. A robust bacterial population that utilized chlorpyrifos as a source of carbon was detected in an Australian soil. The enhanced ability to degrade chlorpyrifos in the Australian soil was successfully transferred to the five United Kingdom soils. Only soils with a pH of >/=6.7 were able to maintain this degrading ability 90 days after inoculation. Transfer and proliferation of degrading microorganisms from the Australian soil to the United Kingdom soils was monitored by molecular fingerprinting of bacterial 16S rRNA genes by PCR-denaturing gradient gel electrophoresis (DGGE). Two bands were found to be associated with enhanced degradation of chlorpyrifos. Band 1 had sequence similarity to enterics and their relatives, while band 2 had sequence similarity to strains of Pseudomonas. Liquid enrichment culture using the Australian soil as the source of the inoculum led to the isolation of a chlorpyrifos-degrading bacterium. This strain had a 16S rRNA gene with a sequence identical to that of band 1 in the DGGE profile of the Australian soil. DNA probing indicated that genes similar to known organophosphate-degrading (opd) genes were present in the United Kingdom soils. However, no DNA hybridization signal was detected for the Australian soil or the isolated degrader. This indicates that unrelated genes were present in both the Australian soil and the chlorpyrifos-degrading isolate. These results are consistent with our observations that degradation of chlorpyrifos in these systems was unusual, as it was growth linked and involved complete mineralization. As the 16S rRNA gene of the isolate matched a visible DGGE band from the Australian soil, the isolate is likely to be both prominent and involved in the degradation of chlorpyrifos in this soil.

Project description:1. Two bacteria, a Bacillus sp. and a Nocardia sp. (strain Z1) were isolated from soil by enrichment with 0.1 percent (v/v) pyridine and grew rapidly on this compound as sole C, N and energy source. The monohydroxypyridines, tetrahydropyridine, piperidine and some other analogues were not utilized for growth or oxidized by washed suspensions of either bacterium. 2. Cell-free extracts were unable to metabolize pyridine even after supplementation with a variety of cofactors or protecting agents. Treatment of cells with toluene led to rapid loss of the ability to oxidize pyridine. 3. In the presence of 10mM-semicarbazide at pH 6.0, Nocardia Z1 accumulated a semialdehyde idenditied as its 2,4-dinitrophenylhydrazone by chromatography, mixed melting point, mass spectrometry and isotope trapping from [2,6(-14)C]pyridine as glutarate semialdehyde. 4. Extracts of this bacterium prepared from cells grown with pyridine or exposed to the gratuitous inducer 2-picoline, contained high activities of a specific glutarate semialdehyde dehydrogenase. 5. Cells grown with pyridine or glutarate also contained a glutaric dialdehyde dehydrogenase, an acyl-CoA synthetase and elevated amounts of isocitrate lyase but no glutaryl-CoA dehydrogenase. 6. Bacillus 4 accumulated in the presence of 10mM-semicarbazide several acidic carbonyl compounds from pyridine among which was succinate semialdehyde. Extracts of this bacillus after growth of the cells with pyridine contained an inducible succinate semialdehyde dehydrogenase in amounts at least 50-fold over those found in succinate-grown cells. 7. Two mutants of this bacillus, selected for their inability to grow on pyridine were deficient in succinate semialdehyde dehydrogenase. 8. In the presence of 0.2mM-KCN, washed suspensions of Bacillus 4 accumulated formate and possibly formamide from pyridine. The use of [14C]pyridine showed that formate was derived from C-2 of the pyridine ring. 9. The organism had a specific formamide amidohydrolase cleaving formamide quantitatively to formate and NH3. 10. Formate was further oxidized by the particle fraction. There was no soluble formate dehydrogenase in extracts.

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Role of soil pH in the development of enhanced biodegradation of fenamiphos.

Publications

Role of soil pH in the development of enhanced biodegradation of fenamiphos.

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